I. Field of the Invention
The present invention relates to the determination of aromatic constituents in hydrocarbons by near infrared spectroscopy and is generally classified in U. S. Patent Office Class 250, subclass 343, 341, and 339.
II. Description of the Prior Art
U.S. Pat. No. 4,963,745 granted Oct. 16, 1990 for octane measuring process and device to S. M. Maggard teaches the use of near infrared absorbance of the methyne band to measure octane, etc. of a fuel by near infrared spectroscopy.
The aforementioned U.S. Ser. No. 506,391 teaches the determination of the constituents of PIANO aromatics (paraffins, aromatics, isoparaffins, naphthenes, and olefins) by near infrared techniques.
U.S. Pat. No. 4,800,279, and the references cited thereon, to Hieftje et al. relates to the determination of properties of hydrocarbons by near infrared absorbance.
European Patent Office 0285251 published filed 10/1988 relates to the general field of analysis by near infrared spectroscopy.
"Near-Infrared Reflectance Analysis by Gauss-Jordan Linear Algebra", D. E. Honigs, J. M. Freelin, G. M. Hieftje, T. B. Hirschfeld, Applied Spectroscopy, vol. 37, no. 6, 1983, pp 491-497, teaches statistical manipulation of NIR spectral data.
"Prediction of Gasoline Octane Numbers from Near Infrared Spectral Features in the Range 660-1215 nm" by J. J. Kelly et al., Analytical Chemistry, vol. 61, no. 4, Feb. 15, 1989, pp 313-320, relates to the prediction of octane. Also by Kelly et al., "Nondestructive Analytical Procedure for Simultaneous Estimation of the Major Classes of Hydrocarbon Constituents of Finished Gasolines", Analytical Chemistry, vol. 62, no. 14, Jul. 15, 1990, pp 1444-1451.
Percents of each of the individual compounds detected by gas chromatography are grouped under their respective generic classifications in the PIANO classification system, and the relative percentage of each of the components paraffins through olefins is determined in weight percent, volume percent, or mole percent as required. An example of this procedure is that taught by Analytical Automation Specialists, Inc., "The Detailed Analysis of Petroleum Naphthas, Reformates, Gasoline and Condensates by High-Resolution Gas Chromatography", Operators Manual, P.O. Box 80653, Baton Rouge, La. 70898. Also available is AAS (Analytical Automated Systems) PIANO Software Package, Sievers Research PIANO Software Package.
Other NIR analysis techniques are taught in J. Prakt. Chem., 317(1), 1-16 by Bernhard and Berthold, who perform structural group analysis of mixtures of saturated and aromatic hydrocarbons, and in the quantitative analysis of benzene-toluene-paraffin mixtures in the near-infrared by Leimer and Schmidt in Chem. Tech. (Leipzig), 25(2), 99-100. "Near-infrared spectroscopy of hydrocarbon functional groups was performed by Tosi and Pinto, Spectrochim ACTA, Part A, 28(3), 585-97, who examined 50 linear and branched paraffins and related the absorbtivities to the concentration of the groups such as CH.sub.3 and CH.sub.2.
Ultraviolet and near-infrared analysis of mixtures of aromatics is taught by Schmidt in Erdoelkohle, Erdgas, Petrochem., 21(6), 334-40, who sought to determine concentrations of specific compounds.
Hydrotreating is taught by many chemical engineering texts. "Reduction of Aromatics in Diesel Fuel" by A. J. Suchanek, National Petroleum Refiners Association, AM-90-21, 1990, provides a brief review.
Other patents which relate to the general field of the invention are U.S. Pat. Nos. 4,277,326; 4,264,336; 3,496,053; 903,020; 4,323,777; 4,433,239; and 4,591,718.
Each of the above references is understood to teach a correlation between the absorbance in the near infrared and some physical or chemical property. None of them teach an absolute determination for a very complex mixture such as diesel fuel, as is involved in the percent aromatics determined by the present invention.
Also none of the references teach the determination of aromatics where GC separations are not possible due to co-elution.